Method of controlling metallic layer etching process and regenerating etchant for metallic layer etching process based on near infrared spectrometer

ABSTRACT

In a method of controlling a metallic layer etching process for fabricating a semiconductor device or a liquid crystal display device, the composition of the etchant used in etching the metallic layer is first analyzed with the NIR spectrometer. The state of the etchant is then determined by comparing the analyzed composition with the reference composition. In case the life span of the etchant comes to an end, the etchant is replaced with a new etchant. By contrast, in case the life span of the etchant is left over, the etchant is delivered to the next metallic layer etching process. This analysis technique may be applied to the etchant regenerating process in a similar way.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method of controlling a metalliclayer etching process and a method of regenerating an etchant for themetallic layer etching process based on a near infrared (NIR)spectrometer and, more particularly, to an NIR spectrometer-basedetching control method and etchant regeneration method whichautomatically analyzes the composition of an etchant used in thelithography process for fabricating a semiconductor device or a liquidcrystal display device in real time, thereby controlling the etchingprocess and regenerating the etchant in an accurate and effective mannerwhile reducing the required period of time therefor.

(b) Description of the Related Art

As a large-size semiconductor device or liquid crystal display devicebecomes to be the choice of electronic consumers, the amount of solventsused in fabricating such a device has been significantly increased. Inthis situation, effective use of the solvents should be made to optimizethe device fabrication process. Among such solvents, etchant is used toetch a metallic layer of chrome or aluminum, on which a photoresistlayer of a predetermined pattern is formed as a mask, so that apatterned metallic layer is formed. After the etching is made, theetchant is recovered, and re-used in the next etching process. As theetchant is repeatedly used, alien materials are continuouslyincorporated into the etchant, and the initial composition of theetchant is continuously altered. When such an alteration degree in theinitial composition exceeds the critical value, the etchant cannot beused for the etching purpose without adjusting the composition. In thiscase, the alien materials should be removed from the etchant, and thecomponents of the etchant exhausted through the etching process shouldbe newly supplied thereto. That is, the etchant should be regeneratedbefore it is reused in the next etching process.

Meanwhile, a conventional way of determining whether the etchant can bestill used for the etching purpose is to observe whether spots or stainsare formed on a substrate during the etching process, therebyidentifying the degree of contamination and variation in the compositionof the etchant. However, with such a technique, the etchant cannot beanalyzed quantitatively and suitably. That is, either the etchant to bewaste-disposed may be used for the etching while causing processfailure, or the etchant to be reused may be waste-disposed.

In the regeneration process of the etchant, the components of theetchant should be analyzed from time to time to regenerate the etchantof a uniform composition. For this purpose, conventionally, the userhimself extracts a sample from the regenerator, and analyzes the samplewith various analytical instruments. However, this method needs muchtime and effort for the analysis. Furthermore, when the requiredcomponents determined by the time-consuming analysis are supplied to theregenerator, the regenerator is liable to be full of the etchant due tothe etchant delivered from the etching process. In this case, part ofthe etchant should be discharged from the regenerator to supply therequired components thereto. Consequently, the operation of theregenerator is discontinuously made, resulting in increased productioncost and time.

Furthermore, in order to analyze various components of the etchant,separate analytic instrument should be used for each component, and theconcentration of the sample should be adjusted to be suitable for eachanalytic instrument, and more than thirty minutes is required for theanalysis. This makes it difficult to perform the desired real-timeanalysis.

In order to overcome such problems, it has been recently proposed thatan on-line analytic equipment should be used for such an etchantanalysis. However, the currently available on-line analytic equipment atbest makes automatic sampling so that the desired real-time etchantanalysis cannot be achieved. Furthermore, with the currently availableon-line analytic equipment, collective information for treating andprocessing the etchant used in the lithography process cannot beobtained in real time. Therefore, there is a demand for a techniquewhere the composition of the etchant can be analyzed in real time, andthe etchant should be appropriately treated on the basis of theanalysis.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofcontrolling a metallic layer etching process which can detect variationin the composition of the etchant and concentration of metallicimpurities in the etchant in real time during the process of fabricatinga semiconductor device or a liquid crystal display device to manage thelife span of the etchant.

It is another object of the present invention to provide a method ofcontrolling a metallic layer etching process which can provide astandard value for the regeneration time or the waste-disposal time ofthe etchant to improve efficiency in use of the etchant while reducingdevice production cost.

It is still another object of the present invention to provide a methodof regenerating an etchant which can analyze composition of the etchantin real time, and control the amount and ratio of the raw materials tobe supplied to a regenerator, thereby obtaining the desired etchanthaving a suitable and uniform composition.

It is still another object of the present invention to provide a methodof controlling a metallic layer etching process and a method ofregenerating an etchant, which can simultaneously analyze variouscomponents of the etchant for a short period of time during the processof fabricating a semiconductor device or a liquid crystal displaydevice, resulting in enhanced analytic efficiency, rapid processing, andimproved quality control.

These and other objects may be achieved by a method of controlling ametallic layer etching process and a method of regenerating an etchantfor the metallic layer etching process based on a near infrared (NIR)spectrometer.

In the metallic layer etching process controlling method, thecomposition of the etchant are first analyzed using the NIRspectrometer. The life span of the etchant is then identified bycomparing the analyzed composition with reference composition. In casethe life span of the etchant comes to an end, the etchant is replacedwith a new etchant. By contrast, in case the life span of the etchant isleft over, the etchant is reused in the next metallic layer etchingprocess.

In the etchant regenerating process, the composition of the etchant in aregenerator for adjusting the composition of the etchant, are firstanalyzed with the NIR spectrometer. The components to be newly suppliedare then identified through comparing the analyzed composition withreference composition. The required components are supplied into theregenerator.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or the similar components, wherein:

FIG. 1 is a block diagram showing the system for controlling a metalliclayer etching process utilizing a NIR spectrometer according to apreferred embodiment of the present invention;

FIG. 2 is a block diagram showing the system for regenerating theetchant utilizing a NIR spectrometer according to a preferred embodimentof the present invention;

FIG. 3 is a graph for showing an example of the light absorptionspectrum of an etchant in the wavelength region of 900–1700 nm measuredby the NIR spectrometer;

FIG. 4 is a graph showing the relation of the true concentration ofacetic acid in an etchant and the concentration of the same obtained bythe NIR spectrometer;

FIG. 5 is a graph showing the relation of the true concentration ofphosphoric acid in an etchant and the concentration of the same obtainedby the NIR spectrometer;

FIG. 6 is a graph showing the relation of the true concentration ofnitric acid in an etchant and the concentration of the same obtained bythe NIR spectrometer; and

FIG. 7 is a graph showing the relation of the true concentration ofwater in an etchant and the concentration of the same obtained by theNIR spectrometer;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention will be explained with referenceto the accompanying drawings.

In the process of fabricating a semiconductor device or liquid crystaldisplay device, an etchant is sprayed onto a substrate sequentiallyoverlaid with a metallic layer and a patterned photoresist so that themetallic layer is etched through the photoresist pattern. Thereafter,the photoresist is removed while leaving the desired pattern at themetallic layer. At this time, the etchant containing the etched metallicresidues is collected in an etchant collection tank placed below thesubstrate. When the amount of etchant in the collection tank reaches apredetermined value, it is delivered to an etchant storage tank by adelivering pump. Since each component of the etchant has itscharacteristic light absorption wavelength, the composition of theetchant can be analyzed in real time by detecting the light absorptionof the etchant at near infrared (NIR) wavelength range with a NIRspectrometer.

The NIR spectrometer-based analysis technique is one of real-timeanalysis techniques recently developed. In the latter half of thenineteen-seventies, a technique of measuring moisture and proteincontents in the wheat with the NIR spectrometer was officiallyrecognized in Canada and U.S.A. Since then, the NIR spectrometer hasbeen used in the fields of fine chemistry, pharmacy, or petrochemicalplant operation automation. For instance, there are various techniquessuch as a technique of controlling yield of olefin in olefinpolymerization through analyzing hydrocarbons contents in the olefinwith NIR spectrometer (Japanese Patent Laid-open Publication No.Hei2-28293), a technique of measuring components of grain in real time(U.S. Pat. No. 5,751,421), a technique of measuring the amount ofisomers of hydrocarbons in real time (U.S. Pat. No. 5,717,209), and atechnique of analyzing the amount of aromatic compounds in hydrocarbonsin real time (U.S. Pat. No. 5,145,785).

The NIR ray used in the NIR spectrometer is a light having wavelength ofabout 700–2500 nm, preferably having frequency of 4,000–12,000 cm⁻¹(about 830–2500 nm), which is an intermediate range between the visibleray of 12,000–25,000 cm⁻¹, and the middle infrared ray of 400–4,000cm⁻¹. Thus, the NIR ray is lower in energy than the visible ray, buthigher than the middle-infrared ray. The energy of the NIR ray iscorrespond to the energy of a combination band and an overtone band ofmolecular vibrational energies of functional groups such as —CH, —OH,and —NH. As the absorption of the NIR ray by the combination band andthe overtone band is significantly weak, variation in the NIR rayabsorption according to the change of the absorption intensity issmaller than that of the middle infrared absorption spectrum by 1/10–1/1000. Therefore, under the application of the NIR ray, the compositionof the sample can be directly analyzed without diluting. Furthermore,due to the overlapping of a plurality of overtone bands and combinationbands, and light absorption by hydrogen bonding or molecularinteraction, quantitative analysis with respect to various components ofthe sample can be performed simultaneously. For the quantitativeanalysis of a multiple-components sample, the ray of NIR wavelengths,which are characteristic to the multiple-components, is radiated to thesample. Then the absorption peaks are monitored, and the concentrationsof each component are derived with reference to a standard calibrationcurve showing the relation of concentration and light absorption of thecomponent. In case the light absorption peaks of the respectivecomponents are overlapped, multiple regression analysis can be carriedout to analyze the effect of each component. Accordingly, the analysisbased on the NIR spectrometer can be rapidly carried out in 1 minute orless even if several components are analyzed simultaneously.

In order to analyze the composition of the etchant in real time with theNIR spectrometer, various techniques can be used. For instance, NIR rayabsorption of the sample can be measured by dipping a detection probeinto an etchant storage tank or into a sample from the etchant storagetank, and by detecting the light absorption of the sample.Alternatively, NIR ray absorption of the sample can be measured byflowing the etchant sample to a flow cell, and by detecting the lightabsorption of the flow cell.

In the technique of using the detection probe, the probe having anoptical fiber cable is dipped into the etchant, and the lightabsorption, which are characteristic to the respective component of theetchant, are analyzed. Thereby, variations of the composition of theetchant, and variations of the concentrations of the metallic residuesdissolved in the etchant are detected. Since, the probe has an NIRradiation and detection parts, the probe can measure light absorption ofthe components at their characteristic wavelengths in real time.

In the technique of using the flow cell, the flow cell has a samplingport which is formed on a regenerator or an etchant storage tank forsampling the etchant therefrom, and the light absorption of the etchantsample is analyzed by the NIR spectrometer, thereby detecting thecomposition of the etchant. In the present invention, in order toanalyze the composition of the etchant in real time with the NIRspectrometer, the two techniques can be selectively used to the etchingprocess of the semiconductor device and liquid crystal display deviceaccording to the temperature of the etchant, the amount of alienmaterials therein etc,

FIG. 1 is a block diagram showing an example of the system forcontrolling a metallic layer etching process utilizing a NIRspectrometer. The controlling system includes an analysis system 100,which includes a temperature control and alien material removal unit 30,a flow cell or probe 40, a multiplexing system 50, an NIR spectrometer60 having an NIR radiation lamp, a monochromator and a detector, and anoutput unit 70. A tungsten-halogen lamp may be used for the NIRradiation lamp, an AOTS(acousto-optical tunable scanning), FT(Fouriertransform) or a grating for the monochromator, and an indium galliumarsenic(InGaAs) or PbS detector for the detector.

In operation, an etchant sample is delivered from the storage tank 10 tothe temperature control and alien material removal unit 30 via a fastloop 20. The temperature control and alien material removal unit 30controls the sample to be at ambient temperature, and removes alienmaterials from the sample. Then, the sample is delivered to the flowcell or probe 40 to perform the NIR absorption analysis. Since the NIRspectrometer 60 produces different analysis results according to thetemperature of the sample, the temperature of the sample should beadjusted to the same temperature with a standard sample, which is usedto make a calibration curve showing the relation of concentration andabsorbance. The NIR spectrometer 60 measures the absorption spectra ofthe sample in the flow cell or probe 40 with its NIR radiation lamp, themonochromator, and the detector. The analysis results are output by wayof the output unit 70. The sample used for the analysis is delivered tothe etchant storage tank 10 through a recovery system 80. As shown inFIG. 1, a multiplexing system 50 is preferably provided to change theflow cell or probe 40 analyzed by the spectrometer 60 in case one NIRspectrometer 60 is used to analyze several samples from multiple processlines. In this case, the analysis system 100 is provided with pluralnumbers of fast loops 20 and flow cells or probes 40 connected to therespective process lines, therefore, the samples from the multipleprocess lines can be analyzed with one spectrometer 60.

In order to quantitatively analyze the composition of the etchant andthe metallic contents dissolved therein, a calibration curve showing therelation of concentration and absorbance of each component should bepreviously made. The calibration curve is made through measuring thelight absorbance of a component of a standard etchant sample whilevarying the concentration of the component. Then the concentration of acomponent in a sample can be determined by comparing the detectedabsorbance with the absorbance of the calibration curve, therebyidentifying the composition of the sample. The analyzed composition iscompared with the reference composition to determine whether the etchantshould be regenerated or reused, in other word, whether the etchant isusable.

In case the amount of each component of the etchant and the metalliccontents dissolved therein does not exceed the reference value, that is,in case the life span of the etchant does not come to an end, a separatedelivering pump is operated to deliver the etchant to the next metalliclayer etching process. By contrast, in case the life span of the presentetchant comes to an end, a new etchant is introduced into the subsequentmetallic layer etching process, and the present etchant is delivered toa regenerator for regeneration of the etchant, or waste-disposed.

In this way, the composition of the etchant is automatically analyzedwith a predetermined time interval using an on-line NIR spectrometersynchronized with the process lines so that the historical recordingwith respect to the composition of the etchant can be established, andthe state of the etchant in the etching process can be quantitativelydetermined. This makes it possible to use the etchant in accurate andeffective manners.

A method of regenerating the etchant using a NIR spectrometer will benow explained with reference to FIG. 2. FIG. 2 is a block diagramshowing the system for regenerating the etchant utilizing a NIRspectrometer. The regeneration system includes the same analysis system100 used in the metallic layer etching process control system.

The method of regenerating the etchant using the NIR spectrometerutilizes the same principle as in the metallic layer etching processcontrol method. The composition of the etchant in a regenerator 110 isanalyzed in real time with the analysis system 100 including the NIRspectrometer 60. It is preferable that the wavelength range of the NIRspectrometer for analyzing the composition is 700–2500 nm. The analyzedcompositions of the etchant are compared with the reference composition,and the components to be newly supplied are identified from thecomparison. In accordance with the identification results, valves 120and 130 are opening to supply the required components to the regenerator110. The regenerator 110 may be operated under low pressure, highpressure, or middle pressure. In this way, the etchant is regeneratedupon receipt of the required components such that it has the samecomposition as the initial etchant. The regenerated etchant is again fedto the metallic layer etching process.

The analysis system 100 can be connected to a controller (not shown),and the controller controls the valves 120 and 130 such that theyautomatically supply the required constituents according to the analysisresult. In the metallic layer etching process, the process automationcan be also applied in the same manner. The components of the etchantthat can be analyzed with the NIR spectrometer include hydrochloricacid(HCl), nitric acid(HNO₃), acetic acid(CH₃COOH), phosphoricacid(H₃PO₄), fluoric acid(HF), oxalic acid((COOH)₂), sulfuricacid(H₂SO₄), cerium ammonium nitrate(CAN), and water, but not limitedthereto.

The following examples are provided just to illustrate the presentinvention in more detail. In the examples, the percentage and themixture ratio represent weight percent and weight ratio.

EXAMPLE 1 to 3

Etchants having the composition (1) to (3) listed below were used in themetallic etching process control system shown in FIG. 1, and thecomposition of the etchant were analyzed in real time in the controllingsystem. The analysis was performed at various concentrations of theetchant components. The results of the analysis are compared with theanalysis results obtained from the conventional analysis method, whichuses various analysis instruments. Namely, in order to evaluate theadequacy of the NIR spectrometer-based analysis for the etching process,the etchant analysis results from the NIR spectrometer were comparedwith the etchant analysis results from the conventional analysis systemover the long time period of seven months. The comparison results arelisted in Table 1.

(1) hydrochloric acid, nitric acid, and water

(2) nitric acid, acetic acid, phosphoric acid, and water

(3) cerium ammonium nitrate, nitric acid, and water

TABLE 1 Phosphoric Component Acetic acid acid Nitric acid WaterMeasurement 5–35 wt % 30–70 wt % 3–30 wt % 5–30 wt % range Correlation0.9999 0.9998 0.9990 0.9999 coefficient (R²) Standard 0.050  0.094 0.174  0.023  deviation (SD)

As known from Table 1, the correlation coefficient in measurement of thepresent NIR analysis system to the conventional analysis system wasappeared to reach 0.9999, and the standard deviation to be at maximumabout 0.17. That is, the present system and the conventional systemproduce substantially the same analysis results.

FIG. 3 is a graph for showing an example of the light absorptionspectrum of the etchant (1) in the wavelength range of 900–1700 nm.FIGS. 4 to 7 are graphs showing the true concentrations of etchantcomponents(acetic acid, phosphoric acid, nitric acid, and water) and theconcentrations obtained through the NIR spectrometer. As known from thegraphs, the concentrations obtained by the NIR spectrometer have goodcorrelation with respect to the true concentration determined byconventional analytical instrument.

As described above, the inventive method of controlling a metallic layeretching process and regenerating the etchant for the etching processbased on an NIR spectrometer makes it possible to accurately analyze thecomposition of the etchant used in the metallic layer etching processfor fabricating a semiconductor device or a liquid crystal displaydevice. Accordingly, the state of the etchant in the process isquantitatively analyzed so that the metallic layer etching process canbe controlled in an effective manner. Furthermore, with the inventivemethod, the etchant used in the metallic layer etching process isregenerated in a reliable manner while reducing the amount ofconsumption of raw materials. In addition, it can be discriminated inreal time whether the etchant is still usable in the process line, andthis makes it possible to significantly enhance process yield.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A method of controlling a metallic layer etching process, the methodcomprising: removing alien material from a sample of an etchant;monitoring, in real time, at a predetermined temperature, absorptionpeaks of the etchant used for etching a metallic layer in the process offabricating a semiconductor device or a liquid crystal display devicewith a near infrared spectrometer, wherein the near infraredspectrometer comprises a light source radiating a ray of wavelengthrange of 700–2500 nm; determining whether a concentration of eachcomponent of the etchant exceeds a corresponding reference value basedon a standard calibration curve of a reference composition showing arelation of concentration and light absorption of each component todetermine whether the etchant is usable; and either replacing theetchant with a new etchant in case the etchant is not usable, or usingthe etchant in a next metallic layer etching process in case the etchantis usable, wherein the etchant includes one or more materials selectedfrom the group consisting of hydrochloric acid, nitric acid, phosphoricacid, fluoric acid, sulfuric acid, cerium ammonium nitride, and water.2. The method of claim 1 wherein the near infrared spectrometercomprises at least one probe, the probe being dipped into an etchantstorage tank to detect the light absorbance of the etchant.
 3. Themethod of claim 1 wherein the near infrared spectrometer measures thelight absorption of at least one flow cell containing the etchantdelivered from an etchant storage tank.
 4. The method of claim 1 whereinthe step of either replacing the etchant with a new etchant or using theetchant in the next metallic layer etching process is performedautomatically by a controller.
 5. A method of regenerating an etchant,the method comprising: removing alien material from a sample of theetchant; monitoring, in real time, absorption peaks of the etchant bydetermining whether concentration of each component of the etchantexceeds a corresponding reference value based on a standard calibrationcurve of a reference composition showing a relation of concentration andlight absorption of each component at a predetermined temperature in aregenerator for adjusting the composition of the etchant with a nearinfrared spectrometer, wherein the near infrared spectrometer comprisesa light source radiating a ray of wavelength range of 700–2500 nm;determining components to be newly supplied to the etchant by comparingthe monitored absorption peaks with peaks of the standard calibrationcurve of the reference composition; and supplying the components intothe regenerator, wherein the etchant includes one or more materialsselected from the group consisting of hydrochloric acid, nitric acid,phosphoric acid, fluoric acid, sulfuric acid, cerium ammonium nitride,and water.
 6. A method of controlling a metallic layer etching process,the method comprising: removing alien material from a sample of anetchant; monitoring, in real time, at a predetermined temperature, aabsorption peaks of the etchant used for etching a metallic layer in theprocess of fabricating a semiconductor device or a liquid crystaldisplay device with a near infrared spectrometer by determining whetherconcentration of each component of the etchant exceeds a correspondingreference value based on a standard calibration curve showing a relationof concentration and light absorption of each component, wherein thenear infrared spectrometer comprises a light source radiating a ray ofwavelength range of 700–2500 nm; automatically adjusting, wheremonitored absorption peaks vary by an amount greater than apredetermined amount from the corresponding reference value, thecomposition to conform with the reference composition, wherein theetchant includes one or more materials selected from the groupconsisting of hydrochloric acid, nitric acid, phosphoric acid, fluoricacid, sulfuric acid, cerium ammonium nitride, and water.
 7. A real timemethod of controlling a metallic layer etching process, wherein a usedetchant includes one or more materials selected from the groupconsisting of hydrochloric acid, nitric acid, phosphoric acid, fluoricacid, sulfuric acid, cerium ammonium nitride, and water, the methodcomprising: removing alien material from a sample of the used etchant;using near infrared spectroscopy in a wavelength range of 700–2500 nm tomonitor absorption peaks of components of the sample; determining if theused etchant is reusable by comparing the absorption peaks of thecomponents of the sample with a standard calibration curve of areference composition showing a relation of concentration and lightabsorption of each component; and automatically adding components to theused etchant, where the used etchant is determined to be reusable, toconform a composition of the used etchant with the referencecomposition.